Induced magnetic moving iron stereophonic phonograph pickup with replaceable stylus assembly and one common pole piece

ABSTRACT

A stereophonic phonograph pickup of the magnetic type is disclosed wherein the stereophonic output is produced by an elongated tubular armature of permeable material pivotally mounted at one end for movement of its opposite end within a triangular cluster of pole pieces. The pole pieces form the terminal portions of two closed path magnetic circuits, each of which is completed through a core having a voltage-generating coil wound thereabout. One of the pole pieces forms a portion of a common leg for both circuits. Magnetomotive force is provided by a stationary permanent magnet, magnetically coupled with the pivotally mounted end of the armature. A capacitance device is coupled between the coils and an inductance device couples the magnetic circuits to minimize crosstalk.

Ilnitecl States Faten Stanton [54] INDUCED MAGNETIC MOVING IRON S'IEREOPHONIC PHONOGRAPI-I PICKUP WITH REPLACEABLE STYLUS ASSEMBLY AND ONE COMMON POLE 211 Appl.No.: 95,562

[52] US. Cl. ..l79/l00.41K, 274/37 [51] Int. Cl ..H04r 11/12 [58] Field oi'Search ..179/100.41 K, 1004] M, 100.41 Z,

179/l00.4l S; 274/37 [56] References Cited UNITED STATES PATENTS 3,546,399 l2/l970 Stanton et a1. ..l79/l00.41 K

[ 1 Fehl29,i972

2,864,897 12/1958 Kaar ..i79/l 00.41 K

Primary ExaminerBemard Konick Assistant ExaminerRaymond F. Cardillo, .lr. AttorneyKane, Dalsimer, Kane. Sullivan & Kurucz 5 7] ABSTRACT A stereophonic phonograph pickup of the magnetic type is disclosed wherein the stereophonic output is produced by an elongated tubular armature of permeable material pivotally mounted at one end for movement ofits opposite end within a triangular cluster of pole pieces. The pole pieces form the terminal portions of two closed path magnetic circuits, each of which is completed through a core having a voltage-generating coil wound thereabout. One of the pole pieces forms a portion of a common leg for both circuits. Magnetomotive force is provided by a stationary permanent magnet, magnetically coupled with the pivotally mounted end of the armature. A capacitance device is coupled between the coils and an inductance device couples the magnetic circuits to minimize crosstalk.

7 Claims, 10 Drawing Figures Patented Feb. 29, 1972 3,646,279

6 Sheets-Sheet 1 /5 INVENTOR M44 75% a. ram/rad @Jdit,

ATTORNEYS Patented Feb. 29, 1972 6 Sheets-Sheet 5 iv Q INVENI OR WALTEQ aJm/ura/u Patented Feb. 29, 1972 6 Sheets-Sheet 4 Patented Feb. 29, 1972 6 Sheets-Sheet 6 ATToRn tYs INDUCED MAGNETIC MOVING IRON STEREOPIIONIC PHONOGRAPH PICKUP WITH REPLACEABLE STYLUS ASSEMBLY AND ONE COMMON POLE PHECE BACKGROUND OF THE INVENTION Magnetic stereophonic phonograph pickups may generally be classified as being either of the moving iron or moving magnet type. Stereophonic pickups of the moving iron type are those in which the source of flux is a stationary permanent magnet, magnetically coupled with a moving armature of permeable material. Such moving iron pickups provide an advantage over moving permanent magnet-type pickups in that the mass of the moving armature may be significantly reduced thereby providing increased compliance of the armature in response to undulations of the stylus in the record groove.

In the past, some stereophonic pickups of the moving iron type have been deficient in the separation of the two output channels because of changes of flux induced in one channel of the stereo output by virtue of motion of the armature in response to undulations of the stylus in the record groove corresponding to the other stereo channel and because of variations in the magnetization of the moving armature.

In application Ser. No. 794,921 filed Jan. 29, 1969 and now US. Pat. No. 3,546,399, wherein I am a coinventor, a moving iron phonograph pickup is disclosed and claimed wherein a quadrangular cluster of pole pieces is utilized along with an inductance compensating device to overcome the aforementioned problems of moving iron pickups. Although this pickup provides satisfactory results and attains the objectives set forth therein, it is a relatively complex device made up of a large number of intricate components and thus is costly and somewhat difficult to produce.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to overcome the difiiculties and disadvantages heretofore encountered with moving iron stereophonic phonograph pickups and to provide an improved stereophonic pickup which will give satisfactory performance over a relatively long period of time and which has a minimum number of parts which may be readily manufactured and assembled.

In order to accomplish the above, the present invention contemplates the provision of a supporting structure having flux path means of permeable material supported thereon for providing two closed path magnetic circuits, each including a common flux path leg terminating in a common pole piece and separate core means having voltage-generating coils mounted thereon, terminating in other pole pieces. The flux path pole piece is in spaced registry with the core pole pieces so that the three pole pieces forming the terminals for the two magnetic circuits form a generally triangular cluster about a common space.

The support structure is further designed to maintain the moving iron armature of a removable and replaceable moving system in position with one end adapted for movement within the common space in response to movement of a stylus tip and the other end held substantially fixed in magnetically coupled relationship with a permanent magnet. The armature is thus maintained in a condition of substantially uniform and consistent magnetic saturation regardless of the position of its associated stylus tip whereby to provide increased sensitivity, linearity of response and channel separation. Further channel separation is attained by the provision of a capacitance device coupled between the two coils and an inductance device electromagnetically coupled between the magnetic circuits to minimize crosstalk signals.

Another aspect of the present invention contemplates the provision of an improved supporting structure including a first molded plastic body part and a second molded plastic body part shaped to accommodate the various elements of the pickup and contoured to interlock with each other to form a unitary supporting structure which positively supports each of the various component parts and thereby prevents relative movement between the magnetic circuit elements so as to enable the pickup to withstand sudden shocks without changing its output characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a perspective view of a magnetic stereophonic pickup embodying the present invention wherein the replaceable stylus assembly is shown separated from the cartridge;

FIG. 2 is an exploded view showing the two molded plastic parts making up the cartridge body of the pickup illustrated in FIG. I;

FIG. 3 is an exploded perspective view of the component parts of the cartridge of the present pickup;

FIG. 4 is a side elevational sectional view of the pickup of the present invention including both the cartridge and stylus assembly viewed in the direction of the arrows on line 4-4 of FIG. 1 (when assembled);

FIG. 5 is a transverse sectional view in the direction of the arrows on the line 5-5 of FIG. 4;

FIG. 6 is a transverse sectional view in the direction of the arrows on the line 66 of FIG. 4;

FIG. 7 is a transverse sectional view in the direction of the arrows on the line 77 of FIG. 4;

FIG. 8 is a transverse sectional view in the direction of the arrows on the line 8-8 of FIG. 4;

FIG. 9 is a transverse sectional view in the direction of the arrows on the line 9-9 of FIG. 4; and,

FIG. 10 is a schematic representation of the crosstalk compensation circuit for the present pickup.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is illustrated in the accompanying drawings wherein corresponding parts bear the same reference numeral throughout the several views. The cartridge is generally of the type employing two magnetic circuits, each of which has a voltage-generating coil associated therewith so that changes in the flux through the circuits result in the generation of a voltage across the associated coil. Changes in the circuit flux, in turn, result from the movement of portions of a moving system in response to the contours of a record groove. Reference is now made to FIG. I in particular wherein the stereophonic pickup of the present invention is shown as including a cartridge body designated generally by the numeral 10 and a removable, replaceable moving system designated generally by the numeral I2. The cartridge body contains the transducer system including the magnetic circuits which respond electrically and magnetically to the motion of the moving system to produce a stereophonic output of two channels through terminal pins which extend rearwardly from the cartridge body. The magnetic circuits, I3 and 15, are illustrated schematically in FIG. 10 and will be described in detail forthwith. The moving system includes a stylus 14 which responds mechanicaily to the undulations of a record groove and an armature which moves in response to the stylus. The entire cartridge body is contained within a casing 13 formed of a material of high permeability which is provided with suitable access openings for the moving system armature and terminal pins. Casing I3 shields the magnetic circuits from stray signals which would otherwise adversely affect the sensitivity of the pickup output. A bracket (not shown) may be secured to the cartridge to provide means for securing the pickup to the player tone arm of a phonograph.

Reference is now made to FIG. 3 wherein the cartridge body and transducer system mounted therein are illustrated. In accordance with the present invention, the cartridge is of a simplified design having a minimum number of parts which can readily be assembled together. Thus, the cartridge body is formed of two parts which support the transducer system, a bottom part 16 and top part 20. A pair of intermediate parts l8 and 1% serve as bobbins for the voltage-generating coils of the transducer system and also cooperate in maintaining the various other components of the transducer system in their required spaced relationship. The various parts l6, l8, l9 and 20 of the cartridge body are formed of a nonmagnetic plastic material such as a medium or high impact polystyrene and are molded with interlocking parts to facilitate assembly.

Still referring to FIG. 3, it may be noted that the present cartridge further includes a magnetic circuit element 22 which comprises a base strap 24 from which three legs extend generally transverse to the plane of the base strap. Two of the legs, 26 and 28, serve as core legs for the first and second output channels respectively. The third leg 30, serves as a flux path return leg for both channels.

The details of the assembly of the cartridge will be discussed in more detail forthwith. For the present, it should be noted that the transducer system also includes a pair of pole piece elements 32 and 34 designed for association with the core legs 26 and 28. Each of the pole piece elements includes a stem portion, 36 and 38, and terminates at one end in an arcuate pole piece, 40 and 42 respectively. Pole pieces 40 and 42 each extend generally transverse to the plane of its associated stem portion. The magnetic circuit element 22 and the pole piece elements 32 and 34 are each formed of a highly permeable material, such as mu-metal.

In addition to the magnetic circuit element 22 and pole piece elements 32 and 34, the transducer system further includes a permanent magnet 44 which serves as a source of flux for the magnetic circuits and a pair of coils 46 and 48 (shown preassembled and wound about shank portions of intermediate parts 18 and 19 respectively). The coils serve to generate the first and second channel output signals in the form of voltages induced therein in response to changes in the flux of their associated magnetic circuits. A pair of terminal pins 50 extend rearwardly from the rear of each intermediate part. Terminal pins 50a and 50b are electrically connected to the ends of coil 46 and pins 50c and 50d (not shown) are connected to the ends of coil 4-8. The pins provide the exterior electrical connection for picking up the output channel signals. ln this connection one pin of each pair (50a and 50d) provides a ground connection and the other pin of each pair carries the active signal. The ground pins are interconnected through a grounding strap which is also connected to the casing, and a capacitor 52 couples the active terminal pins 50b and 500. A single turn device 53 of electrically conducting, nonmagnetic material, such as copper is provided about pole pieces 32 and 34 immediately in front of the coils (see FIG. 4). The device contacts both pole piece stems and extends outwardly a distance sufficient to contact the casing thereby grounding the pole pieces to the casing.

As shown in FIG. 3, intermediate parts 18 and 19 each comprise a mounting plate (54 and 56) from which the terminal pins extend rearwardly and coil bobbins, integral with the mounting plates which extend forwardly, generally perpendicular to the mounting plates. The intermediate parts are further provided with longitudinally extending holes 58 and 60 respectively which pass through the bobbins between the terminal pins. During the assembly of the cartridge, the core legs 26 and 28 of magnetic circuit element 22 are inserted into the bobbins from the rear of mounting plates 54 and d. The holes 58 and 60 are suitably dimensioned to also receive and retain the stem portions 36 and 38 respectively of pole piece elements 32 and 34- which are inserted from the front. in this connection, the size and cross-sectional configuration of holes 58 and 60 is such as to maintain the pole piece stems in abutting and magnetically coupled relationship with core legs 26 and 28 respectively.

The assembled cartridge is illustrated in FIGS. 4 through 8. In FIG. 4, an associated stylus assembly 12 is shown in operable position with the cartridge. As shown in FIG. 7, when the magnetic circuits are assembled in the manner described above, the arcuate pole pieces 40 and 42 project over the front of their associated intermediate parts 38 and 19 and are positively supported in this position by shoulders 62 and 64' of the intermediate parts. The bottom surfaces of intermediate parts 18 and 19 are suitably contoured to receive and support the flux path leg 30 of magnetic circuit element 22. In this connection, it should also be noted that the top surface 66 of the bottom body part 16 is also suitably contoured to receive flux path leg 30 which is arcuate in cross section. Thus, in the assembled cartridge each of the pole pieces is completely surrounded by and supported by plastic stock except, of course, within the common space between the pole pieces. Similarly, the flux path leg and core legs are closely surrounded by plastic stock thereby preventing any relative movement of the transducer system members. As may be further noted, the length of flux path leg 30 is somewhat longer than that of the magnetic circuit core legs 26 and 28 so that when the core legs 26 and 22 and pole piece elements 32 and 34 are inserted through holes 58 and so, as previously described, the pole pieces 44 and 42 register with pole piece 68 forming a triangular cluster about a common opening, as shown in FIG. 7. which registers with the armature opening in the casing.

The bottom molded part 16 includes a pair of spaced grooves 70 extending rearwardly from the forward edge. A complimentary tongue 72 is provided on the top body part to enable the body parts to be interlocked with one another as shown in FIG. 6. Similarly, a grooved slot 74 is provided at the rear of top body part 20 and a tongue 76 is provided at the rear of bottom part 16 to enable the joining of the top and bottom parts. The bottom body part 16 is further provided with a longitudinal recess 78 extending from the front surface. This recess also registers with the armature opening in the casing.

A cutout 80 is provided at the lower edge of the front of the top body part. The cutout 80 and recess 78 cooperate in defining a passageway through which the armature 96 of the moving system may be inserted. The passageway is designed to register with the triangular cluster formed by the pole pieces when the transducer system is inserted within the cartridge body. To this end, both intermediate parts 18 and 19 and the top and bottom parts 20 and 16 are provided with mounting flanges generally designated by the numeral 84 to provide proper alignment of the transducer system within an assembled cartridge and to enable the intermediate parts to be snapfitted into the body parts. A partition 86 extends from the rear wall of the bottom part and cooperates in maintaining the necessary spacing and alignment of the cartridge components.

As shown most clearly in FIG. 4, the top body part 20 includes a vertically elongated magnet-retaining block section 88 at its forward end. A rectangular indentation extends upwardly into the magnet-retaining section 88 and the permanent magnet 44 is housed within the rectangular indentation 90. A generally rectangular aperture 92 is provided in the lower portion 93 of magnet 44 which prevents portions of the magnet from blocking the armature passageway.

The assembly of the present invention consists of first inserting permanent magnet 44 within the magnet-retaining section 88 of the cartridge body top portion 20. The legs 26 and 23 of the magnetic circuit element 22 are then inserted into the holes of the bobbin sections of intermediate parts 18 and 19 from the rear with the flux path leg 30 of element 22 positioned under parts 18 and 19. The pole piece stems 36 and 38 of pole piece elements 32 and 34 are then inserted into the holes in bobbins l8 and 19 from the front with their pole pieces 40 and 42 in aligned registry with pole piece 68 of flux path leg 39. As was previously noted, the configuration of the bobbin holes is such as to insure the magnetic coupling of each core leg of the magnetic element to its associated pole piece stem.

The subassembly consisting of the intermediate parts and their associated portion of the transducer system are then mounted on the body part base 16 with the terminal pins 50, which had previously been connected to the ends of the voltage-generating coils would about bobbins l8 and 19, extending through suitable openings 94 in the rear of base part to. The top part 10 is then positioned over the subassembly and base and locked in place by engagement of tongue and grooves 70 and 72 and 76 and 74. This will position the lower end 93 of magnet 44 in front of the pole piece cluster and aperture 92 aligned with the common space between the pole pieces. Capacitor 52 is then connected between the active terminal pin of each channel and the magnetic casing 13 is placed about the body parts. To this end, the top of the casing is open (as shown in FIGS. 6-9) and a closure 95 of magnetic material is provided to complete the shielding of the magnetic circuits contained therein. The closure consists of a flat sheet of material designed to ride between two channels 97 and 99 on opposite sides of the top surface of the upper body part 20.

As previously mentioned, the transducer system housed within the assembled cartridge includes a triangular array of three pole pieces arranged about a common space. The pole pieces each define the terminal point of a magnetic circuit associated with one output channel. Thus, pole piece 40, pole piece stem 36, core leg 26, base strap 24, flux path leg 30 and pole piece 68 form one magnetic circuit and, pole piece 42, pole piece stem 38, core leg 28, base strap 22, flux path leg 30 and pole piece 63 form one magnetic circuit and, pole piece 42, pole piece stem 38, core leg 28, base strap 22, flux path leg 30 and pole piece 68 form the second magnetic circuit. It should be apparent from the above that pole piece 68, flux path leg 39 and base strap 24 are common to both magnetic circuits. Changes in flux in the first magnetic circuit result in a current being induced in voltage generating coil 46 and changes in flux in the other magnetic circuit result in the induction of a current in coil 48. Since both magnetic circuits extend through the common spacing between the pole pieces, in the presence of a flux source, the flux through each circuit will be dependent on the position of an armature of magnetic material positioned within the common spacing for movement toward and away from the pole piecesv Referring to FIG. 4, it is noted that the present cartridge is designed to accept the moving iron armature of a stylus assembly 12. Such an assembly is described in detail in the previously referred to application Ser. No. 794,921. For the present, it suffices to say that the moving iron armature 96 consists of a tube of magnetic material of high permeability disposed within a tubular casing 98 of nonmagnetic material which is designed to enter the common spacing between the pole pieces through the opening in the casing. A record-engaging stylus 180 is connected to the armature by a stylus support tube 302. A suitable spacer and damping device such as a rubber collar 4 is disposed about the moving iron armature at the end adjacent the stylus so that the entire moving assembly including the stylus Wt), stylus tube 102 and moving iron armature 96 can oscillate in response to modulation of the walls of a record groove with the spacer H04 serving to provide a pivot or fulcrum at the end N6 of the moving iron tube. Since the end 106 of armature 96 is at the pivot point, it remains stationary even when the stylus MM) undulates. The other end we of the armature 96 extends through the common space defined by pole pieces 44), 42 and 68 and serves to complete the magnetic circuits of which these pole pieces form a part.

Magnetomotive force for the magnetic circuit is provided by permanent magnet 44 which is positioned within indentation 90 in the magnet retaining section of the top body part 20. in this position, the lower end 93 of magnet 44 is magnetically coupled to the pivoted end 1% of armature 96 so that there is no relative movement between the armature end 106 and magnet. The degree of magnetic saturation of the armature is thus independent of the position of the armature with respect to the pole pieces. The opposite end N8 of the armature, however, moves to or from pole pieces-40 or 42 (in response to undulations in the record groove) and thereby increases or decreases the flux through the magnetic circuits associated with these pole pieces thereby resulting in a change in the voltage induced coils 46 and 48 related to the undulation of the record groove.

As was previously mentioned, the movement of the armature toward or away from one of the pole pieces results in a signal being induced in the coil associated with that pole piece. However, since both coils are mounted in close proximity to one another there is, unavoidably, some magnetic inductance coupling between them, so that when a load (such as a preamplifier) is imposed on one channel the variation in the signal in the one channel will cause an output signal (crosstalk) in the other channel.

To compensate for the crosstalk, a capacitor 52 is coupled between the coils as shown in FIG. 10 and an inductance device 53 electromagnetically couples the magnetic circuits. Actually, the capacitor is connected between the active terminal pins of the two circuits, as shown in FIG. 3. In practice, a capacitance of between l30pF and lpF was found to satisfactorily minimize crosstalk particularly at the high frequency end of the audio spectrum.

The pole piece grounding strap 53 which is in effect an inductance device electromagnetically coupled between the magnetic circuits serves the additional function of compensating for the crosstalk in the remainder of the audio spectrum. To this end, the strap 53 serves to induce a counter magnetomotive force in the silent channel to the magnetomotive force induced in that channel by the current induced in the active channel during operation. The optimum dimensions for the strap 53 are determined empirically.

Thus, in accordance with the above, the aforementioned objectives have been effectively attained.

Having thus described my invention, what I claim is:

1. A magnetic, stereophonic pickup of the replaceable stylus type including:

a supporting structure comprising a cartridge body;

a transducer system including flux path means terminating in a first pole piece and a pair of core means terminating in second pole pieces disposed and supported within said cartridge body, said flux path means and one of said core means forming a first magnetic circuit and said flux path means and said second core means forming a second magnetic circuit whereby said flux path means and first pole piece is common to both said magnetic circuits and the three pole pieces of said two magnetic circuits form a generally triangular cluster about a common space;

voltage-generating means including a coil mounted on each of said core means;

a moving system removably coupled to said cartridge body including a record engaging stylus, a tubular armature of permeable material extending into said body from one end thereof when said system is in operative position, stylus-connecting means pivotally mounting said armature at one end, said armature one end being outside the common space between the three pole pieces for movement of the opposite end of the armature within the common space formed by the triangular cluster of pole pieces in response to undulation of the stylus when said system is in operative position; and

a flux source including a stationary permanent magnet mounted within said cartridge body proximal said body one end immediately adjacent said armature one end and magnetically coupled at one of its poles to the pivotally mounted end of the armature, whereby the relative motion between the permanent magnet and armature in the region of magnetic coupling is minimal and the armature is maintained in a substantially uniform and constant state of magnetic saturation regardless of the position of the stylus.

2. The stereophonic pickup in accordance with claim 1 further comprising an outer casing of magnetic material disposed about the major portion of said cartridge body and including an opening therein aligned with said common space.

3. The stereophonic pickup of claim 1 wherein said transducer system includes a magnetic circuit element comprising a base member having three prongs extending outwardly therefrom generally perpendicular to the plane of the base member wherein two of said prongs each comprise a portion of one of said core means and said third prong comprises said flux path means, said core means each further including an elongated member generally coextensive with the associated prong and terminating in one of said second pole pieces.

4. The stereophonic pickup as set forth in claim 3 wherein said cartridge body includes a plurality of plastic parts, said plastic parts being contoured to frictionally and tensionally engage with one another to form a unitary structure and said structure closely surrounds said core means, flux path means and pole pieces outside of said common space whereby to prevent any relative movement of the transducer system components.

5. The phonograph pickup of claim 1 further comprising a capacitance device coupling one end of one of said coils to one end of the other of said coils 6. The phonograph pickup of claim 5 further comprising an inductance device eiectrornagnetically coupling said first and second magnetic circuits.

7 The phonograph pickup of claim 6 wherein said inductance device comprises a single turn of electricaily conducting nonmagnetic material in electrical contact with said first and second core means and a casing of magnetic material surrounding said pickup whereby to ground said core means to said casing. 

1. A magnetic, stereophonic pickup of the replaceable stylus type including: a supporting structure comprising a cartridge body; a transducer system including flux path means terminating in a first pole piece and a pAir of core means terminating in second pole pieces disposed and supported within said cartridge body, said flux path means and one of said core means forming a first magnetic circuit and said flux path means and said second core means forming a second magnetic circuit whereby said flux path means and first pole piece is common to both said magnetic circuits and the three pole pieces of said two magnetic circuits form a generally triangular cluster about a common space; voltage-generating means including a coil mounted on each of said core means; a moving system removably coupled to said cartridge body including a record engaging stylus, a tubular armature of permeable material extending into said body from one end thereof when said system is in operative position, stylusconnecting means pivotally mounting said armature at one end, said armature one end being outside the common space between the three pole pieces for movement of the opposite end of the armature within the common space formed by the triangular cluster of pole pieces in response to undulation of the stylus when said system is in operative position; and a flux source including a stationary permanent magnet mounted within said cartridge body proximal said body one end immediately adjacent said armature one end and magnetically coupled at one of its poles to the pivotally mounted end of the armature, whereby the relative motion between the permanent magnet and armature in the region of magnetic coupling is minimal and the armature is maintained in a substantially uniform and constant state of magnetic saturation regardless of the position of the stylus.
 2. The stereophonic pickup in accordance with claim 1 further comprising an outer casing of magnetic material disposed about the major portion of said cartridge body and including an opening therein aligned with said common space.
 3. The stereophonic pickup of claim 1 wherein said transducer system includes a magnetic circuit element comprising a base member having three prongs extending outwardly therefrom generally perpendicular to the plane of the base member wherein two of said prongs each comprise a portion of one of said core means and said third prong comprises said flux path means, said core means each further including an elongated member generally coextensive with the associated prong and terminating in one of said second pole pieces.
 4. The stereophonic pickup as set forth in claim 3 wherein said cartridge body includes a plurality of plastic parts, said plastic parts being contoured to frictionally and tensionally engage with one another to form a unitary structure and said structure closely surrounds said core means, flux path means and pole pieces outside of said common space whereby to prevent any relative movement of the transducer system components.
 5. The phonograph pickup of claim 1 further comprising a capacitance device coupling one end of one of said coils to one end of the other of said coils.
 6. The phonograph pickup of claim 5 further comprising an inductance device electromagnetically coupling said first and second magnetic circuits.
 7. The phonograph pickup of claim 6 wherein said inductance device comprises a single turn of electrically conducting nonmagnetic material in electrical contact with said first and second core means and a casing of magnetic material surrounding said pickup whereby to ground said core means to said casing. 